Electron paramagnetic resonance (EPR) is a powerful and commonly used probe of the electronic structure of metal complexes, in particular metalloproteins. However, due to a lack of appropriate software, many researchers using EPR have not benefitted from the rapid advance of affordable desktop computing power. We propose to develop such software for analysis of complex EPR data. Thus, researchers who would never write their own software could expand their use of EPR. Such a commercial package would help standardize the reporting of EPR results. WEB Research Co. has already developed software for Mossbauer spectroscopy and magnetization saturation. That software has many of the features desired for the EPR software. The new EPR software would include theoretical models for simulations of centers with electronic spin S=1/2 or S is greater than 1/2. Also, sufficient statistical analysis tools would be included to allow realistic estimates of the uncertainties of and correlations between fitted parameters. Our short term (SBIR Phase I) goal is to develop a prototype program and have it evaluated by an independent consultant and a research group. The long term goal is to produce and sell a commercial version that would incorporate extensive help and tutorial features. Such features would make EPR accessible to a broader range of chemists and biochemists.